Mars may seem barren and inhospitable today, but long ago the Red Planet once looked very different. Once upon a time, Mars was warmer than it is now, and covered in rivers, lakes and seas. There’s no way of saying for sure whether Martians ever existed, experts say. Still, there’s mounting evidence that Mars was not only habitable in theory, but actually home to some kind of extraterrestrial life. It’s even possible that remnants of that life still lurk undiscovered beneath Mars’ surface. Here are six reasons why astrobiologists believe in the possibility of life on Mars.
River Valleys and Deltas: Mars’ Incredible Geography
The Martian landscape puts Earth to shame. Its tallest peak, Olympus Mons, towers 85,000 feet (26,000 meters) above the plain surrounding it, according to the European Space Agency. That’s three times taller than Mount Everest. Wide riverbeds snake across the Martian landscape and fan out into deltas. Some of these geological formations can be explained by ancient volcanic activity or Mars’ fierce winds, James W. Head, a geologist at Brown University, wrote in “The Geology of Mars: Evidence from Earth-Based Analogs” (Cambridge University Press, 2007). But others are clearly relics of ancient bodies of water. For instance, apparent riverbeds on Mars tend to end in large craters, the bottoms of which appear flattened. That’s a sign that ancient rivers were depositing sediment there — and that the Martian landscape was once dominated by rivers, lakes and seas.
But the modern consensus that ancient Mars was wet raises an important question: What happened to all that water?